The present invention is generally directed to compositions particularly useful as marking materials in various imaging system, and more specifically the present invention is directed to heterophase ink compositions useful in ink jet printing systems, and to processes for the preparation of these compositions. Accordingly, in one embodiment of the present invention, there are provided heterophase colored ink compositions comprised of an aqueous suspension of dyes covalently attached to component which have been complexed with a hetropolyanion. The aforementioned inks possess excellent waterfastness characteristics, excellent dot and edge definition, and permit decreased ink spreading. Also, the heterophase ink compositions of the present invention enable the print quality of the images generated to be of high resolution, which images are independent of the ink paper interaction, thus allowing these inks to be selected for plain paper marking technologies.
Compositions useful in ink jet printing systems generally contain therein water soluble dyes. Thus, there is disclosed, for example in U.S. Pat. No. 3,846,141, an ink jet composition comprised of an aqueous solution of a water-soluble dye and a humectant material formed of a mixture of a lower alkoxy triglycol, and at least one other compound selected from the group consisting of a poly(ethylene glycol), a lower alkyl ether of diethylene glycol, and glycerol. According to the disclosure of this patent, the printing inks viscosity is subjected to little variation with use as water is lost by evaporation during recirculation of the ink composition through the jet printer. Moreover, apprarently the humectant system disclosed in this patent substantially prevents or minimizes tip dying of the printing ink in the orifice or nozzle during down time of the printer, such as when the printer is rendered inoperative. As further disclosed in this patent, the basic imaging technique in jet printing involves the use of one or more ink jet assemblies connected to a pressurized source of ink. Each individual ink jet includes a very small orifice usally of a diameter of 10 to 200 microns which is energized by magneto restrictive piezo-electric means for the purpose of emitting a continuous stream of uniform droplets of ink at a rate of 33 to 75 kilohertz. This stream of uniform droplets is desirably directed onto the surface of a moving web of, for example, paper; and is controlled to form printed characters in response to video signals derived from an electronic character generator and in response to an electrostatic deflection system; or drop on demand ink propulsion system.
Also, there is disclosed in U.S. Pat. No. 4,279,653 ink jet compositions with water soluble wetting agents a water soluble dye and an oxygen absorber. Similarly, U.S. Pat. No. 4,196,007 describes an ink jet printing composition containing an aqueous solution of a water soluble dye and a humectant consisting of at least one water soluble unsaturated compound. Other prior art disclosing aqueous inks for ink jet printing include U.S. Pat. Nos. 4,101,329; 4,290,072 and 4,299,630. In addition, there is illustrated in U.S. Pat. Nos. 3,705,043; 3,846,141; 4,259,675; and 4,409,040 the use of phosphonates and phosphites, and the use of poly(ethylene glycols) in ink jet marking materials.
Ink compositions for jet printing can be prepared by a number of known methods. Generally, these methods involve dissolving the various dyes, humectants, viscosity control agents, paper fixing additives, surface tension control additives, biocides and anti-oxidants in a known volume of water, followed by adjusting the pH and concentration of the solution to desirable levels. All of the prior art ink compositions disclosed herein are comprised of a solvent vehicle, such as water, ethylene gylcol, and dimethyl sulfoxide; and a molecularly dissolved dye. The dyes selected for these inks must be of a sufficient polarity to enable their dissolution in the solvents selected. Accordingly, images obtained with these ink compositions usually have poor waterfastness characteristics. Additionally, extensive dye and solvent diffusion into the paper substrate causes undersirable ink spreading thereby resulting in low image resolution, and inferior edge acuity.
In those situations wherein the colorants selected are not water soluble, such as those containing pigments, the inks can be prepared by standard known milling processes. However, these pigment dispersions are generally not sufficiently stable; accordingly, when incorporated into a printing machine, the ink particles tend to agglomerate resulting in the clogging of the small nozzles present in the ink jet devices.
Further, in U.S. Pat. No. 3,346,494 there is described a process for preparing stable microemulsions by the addition of a dispersable phase to a continuous phase to which has been added a selected combination of microemulsifiers. Examples of the dispersable phase include liquid hydrocarbons such as benzene, and contain an oil soluble rather than a water soluble dye. The micromulsifier used in the process of the '494 patent is apparently comprised of three ingredients; namely, a fatty acid, an amino alcohol, and an alkyl phenol, reference the disclosure in column 1 beginning at line 64.
Moreover, there is described in copending application U.S. Ser. No. 822,173, the disclosure of which is totally incorporated herein by reference, a heterophase ink composition comprised of a water insoluble polymer dispersed in a liquid medium, the polymer containing therein an oil soluble dye, and a nonionic stabilizer permanently attached thereto. The present invention also uses two-phase ink compositions, however, the solid particles selected are insoluble complexes of dyes and inorganic materials rather than colored polymeric particles. Insoluble complexes selected for the inks of the present invention present several advantages in that, for example, the insoluble aggregates are of a desirable smaller size, from about 0.08 to 0.8 microns average diameter, thus reducing or eliminating clogging of the print head nozzles. Also, the insoluble complexes of the present invention are colored as they are formed, therefore, there is no need for a separate dyeing step. Furthermore, the choice of dye is not restricted to oil-soluble dyes, and the complexes have a high affinity with the paper rendering the prints very permanent through excellent adhesion of the complexes to the paper.
In addition, there is disclosed in U.S. Pat. No. 4,246,154 a process for permitting the formulation of ink jet compositions from vinyl polymer latices by a dye imbibition technique. The aforementioned anionically stabilized latices which are obtained by emulsion polymerization are colored with a dye imbition process. Coloring processes as illustrated in Konishiroku EP Publication No. 0.068,9003 and DE No. 3,233,555 are similar to the '154 patent ink jet procedures with the exception that there is used in the latter a preformed polyurethane latex.
Further, disclosed in copending application U.S. Ser. No. 553,598, entitled Ink Jet Compositions and Processes for Preparation, the disclosure of which is totally incorporated herein by reference, is an ink composition comprised of polymers having dissolved therein oil soluble dyes; and containing surfactants, which composition is dispersed in an aqueous medium. Specifically disclosed in this copending application is an ink composition useful for jet printing processes comprised of a water insoluble polymer dispersed in an aqueous solution, the polymer containing therein an oil soluble dye in an amount of from about 5 percent by weight to about 25 percent by weight; and surfactant particles in an amount of from about 1 percent by weight to about 10 percent by weight. Additionally, disclosed in the aforementioned copending application is a process for the preparation of particles for ink jet printing which comprises (1) providing a monomer having dissolved therein oil soluble dye; (2) dissolving polymerization initiator into the monomer; (3) mixing the resulting solution with water containing a surface active agent therein; (4) subjecting the resulting mixture to ultrasound vibrations while simultaneously or subsequently heating the mixture to affect polymerization, thereby resulting in polymer particles containing the oil soluble dye and surface active agent, which particles are essentially monodispersed and are of a diameter of from about 0.03 micron to about 2 microns. The size of the particles produced in the process of the aforementioned copending application is determined by the mechanical homogenization process while with the process of the present invention particle sizes are dependent primarily on the chemical composition of the reactants. A large variety of dyes can thus be selected since the dyes need not withstand the oxidative environment of a polymerization medium, nor satisfy the solubility requirements related to the dyeing of polymeric particles.
Although the above compositions are suitable for their intended purposes, there continues to be a need for new inks for jet printing, and processes for preparing these compositions. Additionally, there continues to be a need for ink jet compositions which when in use result in superior optical print densities, and have excellent waterfastness characteristics. Moreove, there continues to be a need for inks that contain insoluble dye complexes therein, and wherein these complexes are of desired particle diameter sizes. Further, there is a need for ink compositions with, for example, a diameter of 0.8 micron or less which contain therein insoluble dye complexes and are waterfast, have an excellent affinity for paper substrates, and superior drying times. There is also a need for ink jet compositions with dye complexes wherein the colorant can be localized therein. Also, in accordance with the present invention, there are provided inks desirably containing therein complexed dyes thus enabling the dye to be chemically protected, and further preventing such materials from affecting the surface tension of the particles involved. Additionally, when these compositions impinge the paper substrate during jet printing, there is precipitated immediately on the fibers the ink particles, primarily in view of the colloidal characteristics of these particles. Accordingly, such particles separate from the colorless suspending fluid rather than undesirably penetrating into the paper. With penetration there occurs the known problems of show through, feathering, or chromatographic separation of the dye components. In this regard, it is difficult to prepare waterfast images from water soluble dyes since the ink jet compositions are complex in that in addition to the dyes incorporated therein they contain additives to prevent oxidation thereof, additives for fixing and for controlling viscosity of the liquid ink particles, as well as additives for controlling the evaporation rate and biological activities thereof.
In addition, several of the prior art ink compositions described herein are homogeneous solutions comprised of, for example, a solvent vehicle, such as water, ethylene glycol; and dimethyl sulfoxide; and a molecularly dissolved dye. The dyes selected for these inks must be of a sufficient polarity to enable their dissolution in the solvents selected. Accordingly, images obtained with these ink compositions usually have poor waterfastness characteristics. Additionally, extensive dye and solvent diffusion into the paper substrate causes undesirable ink spreading thereby resulting in low image resolution and inferior edge acuity. The two-phase ink compositions of the present invention resolve these problems.